Apparatus and method for quenching rods and tubes

ABSTRACT

The present invention relates to a apparatus for statically quenching a product ( 1 ) coming from a rolling plant, comprising a seat for housing the product ( 1 ) so that, when the product ( 1 ) is housed there, its main development axis (A) coincides with the positioning axis (Z), a series of nozzles ( 4 ) arranged around the positioning axis (Z), along a curvilinear surface ( 3 ), open at the bottom, and adjustable so as to dispense a flow which is tangential to the surface of the product ( 1 ). The invention also relates to a process for static quenching of the product, implementable by such apparatus.

The present invention relates to a process for quenching products from rolling mills, in particular, for quenching rods and tubes, and to a respective apparatus for implementing it.

At the moment two kinds of quenches are known: the static quench, wherein the body to be quenched is put under the quenching agent, for instance industrial water, along its entire length at the same time, and the so called “progressive” quench, wherein the body to be quenched advances at a suitable speed through the quenching agent flux, so that the tube is quenched progressively along the length.

In detail, static quenching systems, working by immersion, progressive quench systems with nozzles/spray directed radially with respect to the advancing direction of the bar, and progressive quench systems with nozzles directed tangentially with respect to the bar, are known.

Such systems are particularly suitable for quenching bars.

As regards quenching tubes having a thickness of not more than 20 mm, at the moment static quenching systems in tanks, provided with a nozzle for stirring and changing water within the tube, progressive quench systems, having nozzles directed tangentially with respect to the bar and a lance which can be inserted within the same tube, for cooling from its inner surface, and systems for the static quenching having nozzles radially directed with respect to the tube and a nozzle for cooling the inner surface of the tube, are known.

The methods described above propose advantages and drawbacks, when compared with one other. By way of example, progressive quench systems, with lances which can be inserted in the tube offer an optimal heat transfer on the external surface, but have some limit.

For instance, having a lance which can be inserted within the tube, applying such system to tubes having a diameter which is too small, i.e. not allowing lances insertion, is not possible.

The lance, in fact, working counterbalanced, needs to be thick enough to support its weight and to have a diameter suitable for ensuring the necessary water flow. Accordingly, introducing it in tubes having a hole equal to or smaller than its diameter is not possible.

Furthermore, usually the thick rods and tubes have a very low crossing speed. This implies that the material to be quenched may remain for a relatively long time in the room, albeit small, which is between the exit of the furnace and the quenching station, lowering the temperature of the product to be quenched and obviously thus reducing the effect of the quench. For this reason largely increasing the temperature at the exit of the furnace is necessary. Some of the consequences are an undesired increased volume of the austenitic grains, a waste of energy due to overheating of the piece and an increase of the production of flakes.

Furthermore, while quenching bars, due to huge temperature differentials that are generated inside, through cracks often appear. Being in front of pieces that break off from the bar is thus not difficult at all. Detachment of these pieces may occur within the machine, when it is closed, risk damaging the mechanism for rotation of the nozzles.

The object of the present invention is to overcome the drawbacks of the known art and to provide a process for quenching rods and tubes, and a respective apparatus for implementing it, which are more efficient.

This and other purposes are achieved by an apparatus for quenching rods and tubes, according to the attached claim 1, and a respective process for implementing it, according to the attached claim 6; other technical characteristics of detail, according to the present invention, are provided in further dependent claims.

The main object of the invention is an apparatus for static quenching of a product equipped with a main development axis and coming from a rolling plant. The apparatus of the invention comprises a seat for housing the product, or quenching position, equipped with a positioning axis and with a lifting device, suitable for transferring the product to be quenched from the transport means of the treatment plant (roller path outgoing from the furnace) to the main axis of the apparatus, which is vertically placed above the same roller path. In this way, when the product is housed in the quenching position, the main development axis of the product coincides with the main axis of the apparatus.

Furthermore a series of first external nozzles, for dispensing quenching agent, arranged around the positioning axis, is comprised. Advantageously, the first external nozzles are arranged along a curvilinear surface, substantially equidistant from the positioning axis, for instance having a circular cross section, and the first external nozzles are adjustable so as to deliver a flow of quenching agent tangential to the surface of the product.

For this reason, quenching action occurs simultaneously on the whole surface of the product, subjecting it to a flow of liquid always cold, increasing thus efficiency of the static quenching with respect to the one by immersion in tank.

Always according to the invention, the curvilinear surface is open at the bottom.

In such case, advantageously, possible detached pieces due to possible cracks fall freely, with no risk of damaging parts of the apparatus.

A further advantage is the possibility of allowing possible lifting devices, supporting the product and permitting the evacuation, passing.

Furthermore, according to the invention, the apparatus may comprise a second internal nozzle for dispensing quenching agent, arranged in correspondence of the positioning axis, for advantageously quenching the inner surface of a possible tube, having any dimension.

Again, according to the invention, the apparatus may comprise rotating means in order to operate the rotation of a product about the main development axis, when the product is housed in the seat.

In other words, even a series of rotating liftable devices suitable for, thanks to a single and quick lifting, make the positioning axis match with the main development axis of the product and give a rotation to the same product during the quenching, may be comprised.

This permits advantageously obviate the need for nozzles arranged at 360° with respect to the positioning axis: in other words, even if the nozzles were arranged on a curvilinear surface stretches for instance for only 180° with respect to the positioning axis, the rotation of the product permits reaching any point of its surface with the quenching agent.

Furthermore the rotating means permit adjusting the relative speed of the quenching agent when it comes into contact with the product to be quenched: by changing the speed or the direction of rotation, modifying the drastic nature of quenching is possible, for adapting it to the kind of steel to be treated. For the steels susceptible to cracks due to quenching, this possibility is very important.

For instance, providing the rotation in the same direction of the jet, the contact period between the product and the quenching agent is extended, while if the rotation occurs in the opposite direction such contact period decreases.

The nozzles are preferably mounted on lances, providing thus a water flow which is very steady with a relatively low pressure (circa 2,5 bar).

Furthermore, the nozzles may be arranged with an angle between the lines smaller than 15°, as it is apparent in the attached figures: this ensures the possibility of inserting a big total amount of nozzles which are suitable for providing a big water flow.

Another subject of the present invention is a process for static quenching of a product equipped with a main development axis and coming from a plant for treating rolled products, implementable by an apparatus according to the invention and comprising the following steps:

-   -   receiving the product from the plant for treating     -   positioning the product within the apparatus of the invention by         longitudinally moving means and lifting means so that the main         development axis of the product coincides with the positioning         axis of the apparatus, for instance, providing horizontal linear         means of transportation for transporting the product from the         plant for treating to the apparatus, and subsequently vertical         means of transportation for transporting the product into the         working position is possible     -   operating rotating means in order to operate the rotation of the         product about the main development axis, for instance of the         rollers or of the lunettes     -   opening feeding valves of the nozzles for dispensing the         quenching agent and launching the quenching along a curve         tangent to the product and open at the bottom for allowing the         evacuation of possible slivers and pieces detaching from the         same product     -   quenching     -   closing feeding valves     -   stopping rotating means     -   moving the product by moving means in correspondence of a         transporting device.

This permits, advantageously in times shorter than the ones allowed by the known art, obtaining an efficient quenching.

Further aims and advantages of the present invention will become clear from the following description, which refers to an example of embodiment illustrative and preferred, but not limiting, of the apparatus for quenching rods and tubes, and the relative method, according to the present invention, and from the accompanying drawings, wherein:

FIG. 1 shows the apparatus of the invention with the rolled product to be treated on the way;

FIG. 2 shows the apparatus of FIG. 1 with the rolled product in position during the treatment.

The apparatus of the invention has the peculiarity of joining the advantages of the known technologies up to now avoiding the drawbacks.

The apparatus of the invention, in fact, provides a static quenching, so that the product 1 (a tube or a bar) to be quenched is put under the quenching agent 2, for instance water, along its entire length at the same time. Externally, the bar is quenched by a rim 3 of nozzles 4 covering a part of the circumference of the product. The nozzles 4 are adjustable so that the quenching agent 2 hits the product 1 tangentially. The product 1 is housed on rotating devices (rollers or lunettes) 5 and during the step of quenching (FIG. 2) the product 1 rotates about itself along the direction of the narrow R, about its own main development axis, perpendicular to the plane of the figure and passing by the point A. At the head of the apparatus of the invention there is a nozzle, not shown, adequately sized and shaped, which ensures an optimal flow of quenching agent even on the inner surface 6 of the product 1. At the back of the apparatus of the invention there is a hopper 7, collecting the quenching agent 2 coming from the internal nozzle after having crossed the length of the product.

As it is shown in the attached tables, the process of quenching of the invention may comprise the following steps:

-   -   output of the product 1 from the furnace of quenching at an         enough high speed so that the same product 1 does not cool down     -   positioning the product 1 within the apparatus of the invention         by moving rollers 8     -   lifting up the product 1 until the main development axis A of         the product 1 coincides with the main development axis Z of the         apparatus of the invention     -   operating rotating devices 5 in order to operate the rotation of         the product 1 about the axis A     -   opening feeding valves of the nozzles 4 for dispensing the         quenching agent 2 and launching the quenching     -   quenching     -   closing feeding valves.     -   stopping rotating devices 5 and consequently of the rotation of         the product 1     -   pulling down the product in correspondence of a transporting         device (not shown), for instance on rollers     -   evacuating the apparatus for quenching of the invention.

Advantageously, the tangential quenching ensures an optimal exchange on the external surface of the product 1, since the quenching agent 2 hits the product 1 with such a speed that breaks the vapour barrier.

Such efficiency is not vitiated by the absence of nozzles 4 at the bottom. In fact, unlike the existing technologies, wherein the piece is hit on the whole circumference, the piece is rotated about itself at such a speed that compensates the asymmetry of the nozzles. The cooling speed is thus connected to the single conductivity of the steel, the external surface being kept at a temperature which almost coincides with the water temperature. Unlike the traditional systems for progressive quench, the apparatus of the invention provides a quenching agent flow which is tangential to the product 1, i.e. which has not a line symmetry with respect to the axis A of the product 1. The tangential flow, in fact, increases in proportion to the contribution given by each rim 3 of nozzles 4. This permits making the quenching more or less drastic basing on the direction and on the speed of rotation of the product 1. Practically, basing on the direction of rotation R, that as shown in FIG. 2 may be clockwise or counter-clockwise, the difference in the heat exchange is comparable to the difference that there is between a heat exchange in downstream and an exchange occurring in upstream. Unlike the existing technologies, thus making the quenching more or less drastic is possible; for the steels susceptible to the cracks this possibility is very important.

Advantageously, since the bottom part of the machine is open, in case a crack occurs, possible pieces detaching from the product 1 in the machine would not damage nor hit any piece of the machine.

During the quenching the product 1 does not move axially; for cooling the inner surface of the product to be treated, thus, using a not moving nozzle, that does not completely enter within the product 1, is possible as in the case of the lances which are used at the moment for progressive quench. The non moving nozzle is suitable for optimise the inner cooling of the tube, since the section which is available for the cooling water flow coincides with the inner section of the tube, and is not partially obstructed by the lances. 

1-5. (canceled)
 6. Apparatus for statically quenching rods and tubes equipped with a main development axis (A) and coming from a rolling plant, the apparatus comprising a seat for housing a rod or tube equipped with positioning axis (Z), so that when the rod or tube is housed in the seat the main development axis (A) of the rod or tube coincides with the positioning axis (Z), a series of first external nozzles for dispensing quenching agent arranged around the positioning axis (Z), wherein the first external nozzles are arranged along a curvilinear surface, substantially equidistant from the positioning axis (Z), the first external nozzles being adjustable so as deliver a flow of quenching agent tangential to the surface of the rod or tube, wherein longitudinally moving means and lifting means are comprised for positioning the rod or tube coming from the rolling plant so that the main development axis (A) of the rod or tube coincides with the positioning axis (Z), wherein the curvilinear surface has an absence of first external nozzles which defines an opening at the bottom so that the first external nozzles are arranged asymmetrically, that possible detached pieces due to possible cracks fall freely and that the lifting means, supporting the product and permitting the evacuation, pass through the opening at the bottom of the curvilinear surface.
 7. Apparatus for the static quenching according to the claim 6, characterized in that the first external nozzles are arranged on a curvilinear surface stretches for at least 180°, but less than 360°.
 8. Apparatus for static quenching according to claim 6, characterized such that the first external nozzles are angularly spaced about the positioning axis (Z) with a degree less than 15°.
 9. Apparatus for the static quenching according to claim 6, characterized in comprising a second internal nozzle for dispensing quenching agent arranged in correspondence of the positioning axis (Z), for quenching the inner surface of the rod or tube.
 10. Apparatus for the static quenching according to claim 6, characterized in comprising rotating means in order to operate the rotation of a rod or tube about the main development axis (A), when the rod or tube is housed in the seat.
 11. Process for static quenching rods and tubes equipped with a main development axis (A) and coming from a rolling plant, implementable by an apparatus according to claim 6 and comprising the following steps: receiving the rod or tube from the rolling plant positioning the rod or tube within the apparatus by longitudinally moving means positioning the rod or tube within the apparatus by lifting means passing through the bottom of the curvilinear surface so that the main development axis (A) of the rod or tube coincides with the positioning axis (Z) of the apparatus operating rotating means in order to operate the rotation of the rod or tube about the main development axis (A) opening feeding valves of the nozzles for dispensing the quenching agent and launching the quenching along a curve which is tangent to the product and is open at the bottom quenching closing feeding valves stopping rotating means moving the rod or tube by longitudinally moving means and lifting means in correspondence of a transporting device. 